As technology progresses in telecommunications, voice quality of a telephone call is a major concern. For years, service providers operating in the public switched telephone network (PSTN) have implemented various devices to monitor and measure voice quality. Service providers use test equipment placed at various points in their networks to measure transmission parameters associated with voice calls. The test equipment collects data regarding voice calls for subsequent analysis. In some instances, test equipment is sophisticated enough to measure voice calls, make an analysis, and provide the results to an administrator or technician overseeing the test.
In a network as large as the PSTN, service providers have a task to monitor various parts of the network to ensure sufficient voice quality for customers. Unfortunately, test equipment cannot perform the job alone to monitor and measure voice quality. For years, service providers have employed a scheme to embed the functions of their test equipment into telecommunication products. Commercially-available products such as switching equipment and transmission equipment contain various testing functions reducing the need to purchase test equipment separately. For example, a digital switch might include functionality to initiate test calls to a particular destination or another digital switch to measure transmission parameters. With their telecommunications products, service providers can measure voice quality at various points in their network. For example, service providers can make test calls using dedicated circuits in their network. Services providers can also place dedicated equipment in their network to respond to the test calls or perform other types of tests. With this flexibility, a test call can be made all the way to a customer's premise from a remote location such as a telephone exchange (switch).
Monitoring and measuring of voice quality are so important that there are documents covering transmission planning in a PSTN network to monitor, measure, and improve voice quality of a telephone call. The key documents in this area were developed by the International Telecommunications Union (ITU) through its series of documents called recommendations. More particularly, the telecommunication standardization section of the ITU, known as ITU-T, has developed a series of documents covering almost every aspect of telecommunications. Various documents provide information regarding the following: transmission planning that may be employed for a voice network; transmission parameters that may be measured in the voice network; and calculations and analyses that may be performed to obtain results. An overarching goal of ITU-T documents is to provide a uniform way for service providers to interact with each other with their products in a network. Much of the documentation that exists today is focused towards a time division multiplexing (TDM) network associated with the PSTN.
An example of the ITU-T's work includes a document for estimating voice quality called ITU-T RECOMMENDATION G.107, THE E-MODEL, A COMPUTATIONAL MODEL FOR USE IN TRANSMISSION PLANNING (JULY 2002) [hereinafter ITU-T G.107]. This document contains a complex model, known as the ITU-T E-model, with twenty-three (23) parameters for estimating voice quality. The model is complex because the parameters are numerous and change from one voice call to another.
For packet networks, very little, if any, equipment exists to provide testing functions at the level found in the PSTN. This deficiency has been recognized in the industry, and thus, documentation for a packet network has recently began to appear. Many of the gains achieved with the measuring of performance in the TDM network are desired in the packet network. An example of a packet network includes voice over packet (VOP) network. A VOP network may include, but not be limited to, voice over internet protocol (VoIP), voice over asynchronous transfer mode (ATM), voice over frame relay, and VoIP over wireless local area network (LAN).
A lot of work has occurred over the years to determine the parameters that comprise voice quality in a network. Much of the research has culminated into ITU-T Recommendations created for TDM network designers. The ITU-T E-model is a result of that research which was designed to help TDM network designers create sub-networks in the PSTN. With the growth of VOP in the packet network, a solution is needed to apply the concepts included in the ITU-T E-model to packet networks. Service providers operating in a packet network environment would like to be able to measure performance from a location in their network to the customer's premise. They would desire to measure this performance without making test calls, but be able to monitor and measure performance based on the actual telephone calls that occur in the packet network.